The present disclosure relates generally to hematology instruments and detecting liquid levels within containers. For example, containers such as sample tubes or test tubes are often used to contain liquid specimens such as blood plasma. An automatic analyzer may include a probe for taking up a liquid specimen, for example, and further may include a vertically movable mechanism to lower the probe towards a container. In some instances, the probe may have a nozzle formed therein or otherwise coupled to a nozzle. Detecting when the probe contacts the liquid may be desirable. For example, the probe should lower sufficiently to contact the liquid, in which case detecting when such contact occurs is useful. Furthermore, in some cases, immersion too deep within the liquid may be undesirable—e.g., may cause an adverse effect on the result of analysis of the liquid specimen. In such case, detection of the surface level of the liquid is useful. Still further, detection may be important for other purposes—e.g., identifying a liquid level to identify a volume of liquid within the container, etc.